High Temperature-induced Spindle Destabilization Results in Aborted Pollen Production in Populus

High temperature can induce the production of 2n gametes and aborted pollen during microsporogenesis in Populus canescens. However, the mechanism by which high temperature induces pollen abortion remains unknown. Here, pollen abortion was induced by exposing male flower buds of P. canescens to 38 and 41 °C; pollen morphology, meiotic abnormalities, defects of the meiotic microtubular cytoskeleton, and tapetum development were characterized, and expression analysis of the Actin gene was conducted. We found that the dominant meiotic stage, temperature, and duration of treatment significantly affected the percentage of high temperature-induced aborted pollen. Damaged spindle microtubules and depolymerized microtubular cytoskeletons were observed, which resulted in many lagging chromosomes at anaphase Ⅰ and Ⅱ, as well as aneuploid male gametes and micronuclei, generating aborted pollen grains. Tapetum disintegration was also delayed. However, the anther dehisced normally, and some viable pollen grains were released, suggesting that the delayed degradation of the tapetum was not responsible for pollen abortion. A significant reduction in PtActin gene expression was detected in treated cells, indicating that spindle actin was disrupted. The spindle actin appeared to protect cells against chromosome segregation errors during meiosis.

Genomics-based discrimination of 2n gamete formation mechanisms in polyploids: a case study in nonaploid Diospyros kaki ‘Akiou’

Unreduced gametes (2n gametes), possessing double the haploid genome, whatever ploidy that happens to be, are a common source of ploidy variation in plant populations. First and second division restitution (FDR and SDR) are the dominant mechanisms of 2n gamete production; all else being equal, FDR gametes have a higher degree of heterozygosity, thus they are advantageous in breeding. The discrimination of these mechanisms from the consequence of hybridization is challenging, especially in higher polyploids, and usually requires information on centromere location. In this study, we propose a genotyping-based strategy to uncover the mechanisms of 2n gamete formation in progeny that has a higher ploidy than its parents. Simulation of 2n gamete production revealed that FDR and SDR pathways can be discriminated based on allele transmission patterns alone without information on centromere location. We applied this strategy to study the formation mechanism of a nonaploid Diospyros kaki ‘Akiou’, which was bred via hybridization between D. kaki hexaploid cultivars. The result demonstrated that ‘Akiou’ was derived from the fertilization of a normal female gamete by a 2n male gamete, and that this 2n gamete was produced through FDR. Consequently, the distinct duplex transmission pattern in the FDR gamete enabled us to infer the genomic characteristics of polyploid persimmon. The method could be tested only for the plant being polypoid, which allows for the ability to discriminate causes of 2n gamete formation using allele dosage in progeny, and will be useful in future studies of polyploid genomics.

Induced Polyploidy: A Tool for Forage Species Improvement

Polyploidy means having more than two basic sets of chromosomes. Polyploid plants may be artificially obtained through chemical, physical and biological (2n gametes) methods. This approach allows an increased gene scope and expression, thus resulting in phenotypic changes such as yield and product quality. Nonetheless, breeding new cultivars through induced polyploidy should overcome deleterious effects that are partly contributed by genome and epigenome instability after polyploidization. Furthermore, shortening the time required from early chromosome set doubling to the final selection of high yielding superior polyploids is a must. Despite these hurdles, plant breeders have successfully obtained polyploid bred-germplasm in broad range of forages after optimizing methods, concentration and time, particularly when using colchicine. These experimental polyploids are a valuable tool for understanding gene expression, which seems to be driven by dosage dependent gene expression, altered gene regulation and epigenetic changes. Isozymes and DNA-based markers facilitated the identification of rare alleles for particular loci when compared with diploids, and also explained their heterozygosity, phenotypic plasticity and adaptability to diverse environments. Experimentally induced polyploid germplasm could enhance fresh herbage yield and quality, e.g., leaf protein content, leaf total soluble solids, water soluble carbohydrates and sucrose content. Offspring of experimentally obtained hybrids should undergo selection for several generations to improve their performance and stability.

Induced Polyploidy: A Tool for Forage Species Improvement

Polyploidy means having more than two basic sets of chromosomes. Polyploid plants may be artificially obtained through chemical, physical and biological (2n gametes) methods. This approach allows an increased gene scope and expression, thus resulting in phenotypic changes such as yield and product quality. Nonetheless, breeding new cultivars through induced polyploidy should overcome deleterious effects that are partly contributed by genome and epigenome instability after polyploidization. Furthermore, shortening the time required from early chromosome set doubling to the final selection of high yielding superior polyploids is a must. Despite these hurdles, plant breeders have successfully obtained polyploid bred-germplasm in broad range of forages after optimizing methods, concentration and time, particularly when using colchicine. These experimental polyploids are a valuable tool for understanding gene expression, which seems to be driven by dosage dependent gene expression, altered gene regulation and epigenetic changes. Isozymes and DNA-based markers facilitated the identification of rare alleles for particular loci when compared with diploids, and also explained their heterozygosity, phenotypic plasticity and adaptability to diverse environments. Experimentally induced polyploid germplasm could enhance fresh herbage yield and quality, e.g. leaf protein content, leaf total soluble solids, water soluble carbohydrates and sucrose content. Offspring of experimentally obtained hybrids should undergo selection for several generations to improve their performance and stability.

Scope of Whole Genome Duplication in Forages: A Plant Breeder Perspective

Polyploidy is a condition of having more than two sets of chromosomes. Polyploid plants may be artificially obtained through chemical, physical and biological methods (2n gametes). It is considered an interesting approach due to increased genescope and expression, thus resulting in phenotypic changes, such as yield and product quality. Nonetheless, breeding new cultivars through induced polyploidy should overcome deleterious effects partly contributed by genome and epigenome instability after polyploidization. Furthermore, shortening the time required from early chromosome set doubling to the final selection of high yielding superior polyploids is a must. Despite these hurdles, plant breeders have successfully obtained polyploid bred-germplasm in broad range of forages from optimized application methods, concentration and time mainly using colchicine. These experimental polyploids proved to be a valuable tool for understanding gene expression that is driven by dosage dependent gene expression, altered gene regulation and epigenetic changes. Isozymes and DNA-based markers aided on the identification of rare alleles for particular loci when compared with diploids, which may explain their heterozygosity, phenotypic plasticity and adaptability to diverse environments. It has also been observed that experimentally induced polyploid germplasm could enhance fresh herbage yield and quality, e.g. leaf protein content, leaf total soluble solids, water soluble carbohydrates and sucrose content. Offspring of experimentally obtained hybrids underwent selection for several generations to improve their performance and stability.

Sorghum bicolor x S. halepense interspecific hybridization is influenced by the frequency of 2n gametes in S. bicolor

Tetraploid johnsongrass [Sorghum halepense (L.) Pers.] is a sexually-compatible weedy relative of diploid sorghum [Sorghum bicolor (L.) Moench]. To determine the extent of interspecific hybridization between male sterile grain sorghum and johnsongrass and the ploidy of their progeny, cytoplasmic (CMS), genetic (GMS) and chemically induced male sterile lines of Tx623 and Tx631 were pollinated with johnsongrass pollen. At maturity 1% and 0.07% of the developing seeds of Tx623 and Tx631 respectively were recovered. Ninety-one percent of recovered hybrids were tetraploid and two percent were triploid, the tetraploids resulting from 2n gametes present in the sorghum female parent. Their formation appears to be genotype dependent as more tetraploids were recovered from Tx623 than Tx631. Because a tetraploid sorghum x johnsongrass hybrid has a balanced genome, they are male and female fertile providing opportunities for gene flow between the two species. Given the differences in 2n gamete formation among Tx623 and Tx631, seed parent selection may be one way of reducing the likelihood of gene flow. These studies were conducted in controlled and optimum conditions; the actual outcrossing rate in natural conditions is expected to be much lower. More studies are needed to assess the rates of hybridization, fitness, and fertility of the progeny under field conditions.